Light source optical system, light source device, light source unit, and image display apparatus

ABSTRACT

A light source optical system includes: a first optical system configured to guide a first light beam having a first wavelength emitted from a light source to a wavelength conversion element; the wavelength conversion element configured to convert the first light beam into a second light beam having a second wavelength different from the first wavelength, and emit the second light beam; and a second optical system through which the second light beam emitted from the light conversion element passes. The second optical system includes a light guide element configured to guide a portion of the second light beam from one end surface of the light guide element to the other end surface of the light guide element to separate the portion of the second light beam from the second light beam.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35U.S.C. § 119(a) to Japanese Patent Application No. 2020-196706, filed onNov. 27, 2020 and Japanese Patent Application No. 2021-139519, filed onAug. 30, 2021 in the Japan Patent Office, the entire disclosures ofwhich are incorporated by reference herein.

BACKGROUND Technical Field

The present disclosure relates to a light source optical system, a lightsource device, a light source unit, and an image display apparatus.

Related Art

Projectors (image display devices and image projection devices) thatmagnify and project various images onto a screen are widely used. Inprojectors, light emitted from a light source is condensed on an imagedisplay element, or spatial light modulation element such as a digitalmicromirror device (DMD) or a liquid crystal display element, and lightmodulated in accordance with a video signal and emitted from the imagedisplay element is displayed as a color image on a projection surfacesuch as a screen.

Projectors in many cases use, for example, an ultra-high pressuremercury lamp having high brightness as a light source. However, the lifeof such a lamp is shorter and frequent maintenance is required. Inrecent years, the number of projectors using a laser or a light emittingdiode (LED) as a light source, instead of the ultra-high pressuremercury lamp, is growing. Such projectors using a laser or an LED as alight source have a longer life and higher color reproducibility due toits monochromaticity than the ultra-high mercury lamp.

SUMMARY

A light source optical system includes: a first optical systemconfigured to guide a first light beam having a first wavelength emittedfrom a light source to a wavelength conversion element; the wavelengthconversion element configured to convert the first light beam into asecond light beam having a second wavelength different from the firstwavelength, and emit the second light beam; and a second optical systemthrough which the second light beam emitted from the light conversionelement passes. The second optical system includes a light guide elementconfigured to guide a portion of the second light beam from one endsurface of the light guide element to the other end surface of the lightguide element to separate the portion of the second light beam from thesecond light beam.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic view of an entire configuration of a projector(image display apparatus);

FIG. 2 is a schematic view of a configuration of a light source deviceaccording to a first embodiment;

FIG. 3A is a front view of a configuration of a phosphor wheel in thelight source device in FIG. 2;

FIG. 3B is a cross-sectional view of the phosphor wheel in FIG. 3A;

FIG. 4A is a side view of a configuration of a light guide elementaccording to the first embodiment;

FIG. 4B is an enlarged view of a cross section of the light guideelement in FIG. 4A;

FIG. 5 is a front view of a configuration of the light guide elementaccording to the first embodiment;

FIG. 6 is an illustration of an illuminance distribution for the lightsource device according to the first embodiment;

FIG. 7 is an illustration of a light source device according to a secondembodiment;

FIG. 8 is a side view of a configuration of a light guide elementaccording to the second embodiment;

FIG. 9 is a front view of a configuration of the light guide elementaccording to the second embodiment;

FIG. 10 is an illustration of an illuminance distribution for the lightsource device according to the second embodiment;

FIG. 11 is a front view of a configuration of a light guide element inthe light source device according to a third embodiment;

FIG. 12 is a schematic view of a configuration of a light source deviceaccording to a fourth embodiment;

FIG. 13 is a side view of a configuration of a light guide elementaccording to the fourth embodiment;

FIG. 14 is a front view of a configuration of the light guide elementaccording to the fourth embodiment;

FIG. 15 is an illustration of an illuminance distribution for the lightsource device according to the fourth embodiment; and

FIG. 16 is a schematic view of a configuration of a light source deviceaccording to a fifth embodiment.

The accompanying drawings are intended to depict embodiments of thepresent disclosure and should not be interpreted to limit the scopethereof. The accompanying drawings are not to be considered as drawn toscale unless explicitly noted. Also, identical or similar referencenumerals designate identical or similar components throughout theseveral views.

DETAILED DESCRIPTION

In describing embodiments illustrated in the drawings, specificterminology is employed for the sake of clarity. However, the disclosureof this patent specification is not intended to be limited to thespecific terminology so selected and it is to be understood that eachspecific element includes all technical equivalents that operate in asimilar manner and achieve similar results.

Referring now to the drawings, embodiments of the present disclosure aredescribed below. As used herein, the singular forms “a,” “an,” and “the”are intended to include the plural forms as well, unless the contextclearly indicates otherwise.

Embodiments of the present disclosure provide a light source opticalsystem, a light source unit, a light source device, and an image displayapparatus that achieves an improvement in an illuminance distributionwith a simple configuration.

Hereinafter, embodiments of the present invention are described withreference to the drawings. FIG. 1 is a schematic view of the entireconfiguration of a projector as an example of an image displayapparatus. FIGS. 2 to 16 illustrate embodiments of the light sourcedevice as a light source unit refers to. Specifically, FIGS. 2 to 6illustrate a first embodiment, and FIGS. 7 to 10 illustrate a secondembodiment. FIG. 11 illustrates a third embodiment, and FIGS. 12 to 15illustrate a fourth embodiment. Further, FIG. 16 illustrates a fifthembodiment refers to.

In projectors, a color image is formed by irradiating an image displayelement such as a DMD with color light, for example red, green, and blue(i.e., three primary colors of light). These three colors can begenerated by using laser light source for the colors. However, this isnot desirable because luminous efficacies of a green laser and a redlaser are lower than efficacy of a blue laser. Thus, a method using aphosphor and a blue laser as excitation light is used. In the method,the phosphor is irradiated with blue light emitted by the blue laser togenerate fluorescence (i.e., wavelength conversion), which generatedgreen light and red light.

A projector 10 illustrated in FIG. 1 includes a housing 11, a lightsource device 12 as a light source unit, a light uniformizing element13, an illumination optical system 14, an image display element 15, anda projection optical system 16. All these elements, the light sourcedevice 12, the light uniformizing element 13, the illumination opticalsystem 14, the image display element 15, and the projection opticalsystem 16 are housed in the housing 11.

The light source device 12 emits light beams including wavelengthscorresponding to, for example, red (R), green (G), and blue (B) colors.The inner configuration of the light source device 12 is described laterin detail.

The light uniformizing element 13 mixes and uniformizes light beamemitted from the light source device 12. The light uniformizing element13 is, for example, a hollow light tunnel enclosed by four mirror platesfacing inside, a rod integrator having geometry of a cylinder or a prismof transparent material such as glass, or a fly-eye lens in whichmultiple lenses are arrayed in two dimensions.

The illumination optical system 14 substantially uniformly illuminatesthe image display element 15 with the light beam uniformized by thelight uniformizing element 13. The illumination optical system 14includes, for example, at least one lens and one optical element havingat least one reflection surface.

The image display element 15 is, for example, a light valve such as adigital micromirror device (DMD), a transmissive liquid crystal panel,or a reflective liquid crystal panel. The image display element 15modulates light (i.e., light from the light source device 12) passedthrough the illumination optical system 14 and forms an image with themodulated light.

The projection optical system 16 magnifies and projects the image formedby the image display element 15 onto a screen 17 (e.g., projectionsurface) disposed outside the projector 10. The projection opticalsystem 16 includes, for example, at least one lens.

FIG. 2 is a schematic view of a configuration of a light source device12 according to a first embodiment. The light source device 12 includesa laser light source group 20 (light source group), a collimator lensgroup 21, a first lens group 22, a light guide element 23, aquarter-wave plate 24, a second lens group 25, a phosphor wheel 26(wavelength conversion element), a third lens group 27, and a colorwheel 28, which are arranged in this order along a light propagationdirection. For example, components of the light source device 12 otherthan the laser light source group 20 constitute the light source device12 excluding the laser light source group 20.

The laser light source group 20 includes at least one laser light source(solid-state light source). The collimator lens group 21 includes atleast one collimator lens. In FIG. 2, six light sources arranged in adirection parallel to an optical axis of the second optical system(i.e., parallel to the propagation direction of YL, BL (P-POLARIZEDLIGHT) is depicted. Moreover, additional six light sources are arrangedin n rows, where n is an integer of 2 or more, in a directionperpendicular to the drawing sheet in which FIG. 2 is illustrated. Thus,6×n light sources are two-dimensionally arrayed. There is a latitude inthe number of laser light sources in the laser light source group 20.The laser light source group 20 may be, for example, a single laserlight source having high power instead of multiple laser light sources.

Multiple laser light sources in the laser light source group 20 may bearranged in two-dimensional array on a substrate (i.e., two-dimensionallight source array) as a light source unit, but there is a latitude in aspecific aspect thereof. Hereinafter, the laser light source group 20may be referred to as “the two-dimensional light source array”.

The two-dimensional light source array emits, for example, blue laserlight in a wavelength band of blue having a central wavelength of 455nm, which is excitation light BL (i.e., first color light) that excitesa phosphor provided in a phosphor region 26 d (i.e., awavelength-conversion region) in the phosphor wheel 26 in FIGS. 3A and3B. The blue laser light emitted by the two-dimensional light sourcearray (the laser light source group 20) is linearly polarized and has aconstant polarization state. The blue laser light is s-polarized lightwith respect to an incident surface (a front surface 23 a to bedescribed later) of the light guide element 23. The blue laser lightemitted by the two-dimensional light source array (the laser lightsource group 20) is coherent light. The excitation light BL emitted bythe laser light source group 20 may be light having a wavelength toexcite the phosphor in the phosphor region 26 d of the phosphor wheel26, but is not limited to light having the wavelength band of blue.

Multiple collimator lenses of the collimator lens group 21 in FIG. 2 aretwo-dimensionally arrayed and correspond to the multiple laser lightsources of the two-dimensional light source array (the laser lightsource group 20). Multiple collimator lenses of the collimator lensgroup 21 are adjusted to collimate or converge the light (i.e.,excitation light BL) emitted from the multiple laser light sources ofthe two-dimensional light source array (i.e., the laser light sourcegroup 20) to generate parallel light or convergent light. The number ofthe collimator lenses of the collimator lens group 21 coincides with thenumber of laser light sources of the laser light source group 20, andthe number of the collimator lenses may be increased or decreased inproportional to the number of light sources of the laser light sourcegroup 20.

The first lens group 22 has a positive power as a lens group andincludes a positive lens 22 a and a negative lens 22 b in this orderalong a light propagation direction from the laser light source group 20to the phosphor wheel 26. The excitation light BL emitted from thecollimator lens group 21 is parallel light or converging light andenters the first lens group 22. The first lens group 22 guides theexcitation light BL to the light guide element 23 while converging theexcitation light BL. The first lens group 22 may have a negative powerinstead of a positive power as a lens group.

The light guide element 23 is disposed in an optical path between thefirst lens group 22 and the second lens group 25. The light guideelement 23 is, for example, a polarization beam splitter of a flat plateand has a coating that reflects s-polarized light (i.e., first polarizedlight component) in the wavelength band of the excitation light BLguided from the first lens group 22 and transmits p-polarized light(i.e., second polarized light component) in the wavelength band of theexcitation light BL and the fluorescent light YL (second color light)emitted from the phosphor wheel 26.

In the present embodiment, the light guide element 23 reflects thes-polarized light in the wavelength band of the excitation light BL andtransmits the p-polarized light in the wavelength band of the excitationlight BL. Alternatively, the light guide element 23 may reflect thep-polarized light in the wavelength band of the excitation light BL andtransmit the s-polarized light in the wavelength band of the excitationlight BL.

The quarter-wave plate 24 (¼ wavelength plate) is arranged to have itsoptical axis (i.e., fast axis or slow axis of the quarter-wave plate 24)tilted by 45 degrees with respect to the linearly polarized light of theexcitation light BL reflected by the light guide element 23. Thequarter-wave plate 24 converts the excitation light BL reflected by thelight guide element 23 from the linearly polarized light into circularlypolarized light.

The second lens group 25 has positive power as a lens group and includespositive lenses 25 a and 25 b in this order along the light propagationdirection from the laser light source group 20 to the phosphor wheel 26.The excitation light BL is converted into circularly polarized light bythe quarter-wave plate 24 and enters the second lens group 25. Thesecond lens group 25 guides the excitation light BL to the phosphorwheel 26 while converging the excitation light BL.

The excitation light BL guided from the second lens group 25 hits thephosphor wheel 26. FIGS. 3A and 3B are illustrations of theconfiguration of the phosphor wheel 26. The phosphor wheel 26 includes adisc member 26 a and a driving motor 26 c that rotates the disc member26 a about a rotational axis 26 b. The disc member 26 a is, for example,a transparent substrate or a metal substrate such as an aluminumsubstrate, but is not limited thereto.

In the disc member 26 a of the phosphor wheel 26, a major portion of thedisc member 26 a in the circumferential direction (e.g., an angularrange of larger than 270 degrees in the present embodiment) is aphosphor region 26 d, and the remaining portion of the disc member 26 ain the circumferential direction (e.g., an angular range of smaller than90 degrees in the present embodiment) excluding the phosphor region 26 dis an excitation light reflection region 26 e that reflects theexcitation light BL (FIG. 3A).

The phosphor region 26 d includes a reflection coating 26 d 1, aphosphor layer 26 d 2, and an antireflection coating 26 d 3 layered inthis order from the bottom, or the disc member 26 a (FIG. 3B).

The reflection coating 26 d 1 has a property of reflecting light in awavelength band of the fluorescent light YL emitted by the phosphorlayer 26 d 2. When a metal substrate having higher reflectivity is usedfor the disc member 26 a, the reflection coating 26 d 1 may be omitted(i.e., the disc member 26 a has a function of reflecting light such asthe reflection coating 26 a 1).

The phosphor layer 26 d 2 is, for example, a layer in which a phosphormaterial is dispersed at least one of an organic binder and an inorganicbinder, a layer in which a phosphor material is directly crystalized, ora layer including rare earth phosphors such as Ce:YAG. As a wavelengthband of the fluorescent light YL emitted by the phosphor layer 26 dd 2,for example, yellow, blue, green, or red can be used. In the presentembodiment, the fluorescent light YL having a wavelength band of yellowis used. In the present embodiment, a phosphor is used as the wavelengthconversion element, but a phosphorescent material or a nonlinear opticalcrystal may be used.

The antireflection coating 26 d 3 has a property of preventingreflection of light on a surface of the phosphor layers 26 d 2.

On the excitation light reflection region 26 e of the excitation lightBL, a reflection coating 26 e 1 is laminated. The reflection coating 26e 1 has a property of reflecting light in a wavelength band of theexcitation light BL guided from the second lens group 25. When a metalsubstrate having higher reflectivity is used for the disc member 26 a,the reflection coating 26 e 1 may be omitted (i.e., the disc member 26 aserves to reflect light such as the reflection coating 26 a 1).

An irradiation area on the phosphor wheel 26, which is irradiated withthe excitation light BL, moves with time as the disc member 26 a isrotated by the driving motor 26 c. As a result, the excitation light BLincident on the phosphor wheel 26 is divided by time (i.e.,time-division manner) into two states: a state in which the excitationlight BL is converted into the fluorescence light YL having a wavelengthdifferent from the wavelength of the excitation light BL in the phosphorregion 26 d and the fluorescence light YL is emitted; and a state inwhich the excitation light BL incident on the phosphor wheel 26 isreflected by the excitation light reflection region 26 e and emittedfrom the phosphor wheel 26 as is.

There is a latitude in the number and the angular range of the phosphorregion 26 d and the excitation light reflective region 26 e, and variousdesigns are possible. For example, two fluorescent regions and twoexcitation light reflection regions may be alternately arranged atintervals of 90 degrees in the circumferential direction of the phosphorwheel 26.

Referring back to FIG. 2, the light source device 12 is described. Theexcitation light BL reflected by the excitation light reflection region26 e of the phosphor wheel 26 has a reverse circular polarizationdirection (i.e., right-handed circular polarization to left-handedcircular polarization or left-handed circular polarization toright-handed circular polarization) and propagates from the phosphorwheel 26 to the light guide element 23. The circular polarized light(i.e., the excitation light BL) reflected by the excitation lightreflection region 26 e is converted into substantially parallel lightfrom a divergent light by the second lens group 25 and is then convertedinto p-polarized light by the quarter-wave plate 24. The excitationlight BL converted into the p-polarized light passes through the lightguide element 23 and enters the color wheel 28 through the third lensgroup 27 that condenses light. In the embodiment, the third lens group27 includes a single lens.

The excitation light BL incident on the phosphor region 26 d of thephosphor wheel 26 is converted into the fluorescent light YL, and thefluorescent light YL is emitted from the phosphor region 26 d. Thefluorescent light YL emitted by the phosphor region 26 d is convertedinto a substantially parallel light beam from a divergent light beam bythe second lens group 25 and passes through the quarter-wave plate 24and the light guide element 23 to enter the color wheel 28 through thethird lens group 27.

The color wheel 28 includes a disc member 28 a and a driving motor 28 bthat rotates the disc member 28 a about a rotational axis 28 c. The discmember 28 a has a blue region, a yellow region, a red region, and agreen region partitioned in a circumferential direction. The blue regionis synchronized with the excitation light reflection region 26 e of thephosphor wheel 26, and the yellow region, the red region, and the greenregion are synchronized with the phosphor region 26 d of the phosphorwheel 26. The yellow region transmits light having a wavelength band ofyellow as is, which is emitted from the phosphor wheel 26. The redregion and the green region are provided with one or more dichroicmirrors to allow the color wheel 28 to selectively transmit light of redcolor or green color from the wavelength band of yellow (i.e., light ofthe other colors excluding red color and green color is reflected by thedichroic mirrors). As a result, high-purity color light is obtained.

As illustrated in FIG. 1, light of each color produced by the colorwheel 28 in the time-division manner is guided (irradiated) from thelight uniformizing element 13 to the image display element 15 throughthe illumination optical system 14 and forms an image corresponding toeach color. The image corresponding to each color is magnified andprojected on to the screen 17 by the projection optical system 16. As aresult, a color image is formed. In other words, the image displayelement 15 modulates light from the light source device 12 to form animage, and the projection optical system 16 magnifies and projects theimage formed by the image display element 15 onto the screen 17.

In the light source optical system of the light source device 12 in theprojector 10 described above, a first optical system includes the firstlens group 22, the light guide element 23, the quarter-wave plate 24,and the second lens group 25, forming an optical path through which afirst light beam emitted by the laser light source group 20 passes tothe phosphor wheel 26. The first optical system may include thecollimator lens group 21.

In the light source optical system of the light source device 12, asecond optical system includes the second lens group 25, thequarter-wave plate 24, the light guide element 23, and the third lensgroup 27, forming an optical path through which a second light beamhaving the wavelength converted by the phosphor wheel 26 (i.e., a secondlight beam wavelength-converted from the first light beam by thewavelength conversion element) passes. The optical axis LX of the secondoptical system is illustrated in FIGS. 4A, 4B and 5. The second lightbeam LF is illustrated in FIGS. 2, 4A and 5. FIG. 5 is a front view ofthe light guide element 23 along the optical axis LX as viewed from thephosphor wheel 26.

The light guide element 23 works as a reflection element that reflectsthe first light beam entered from the first lens group 22 toward thephosphor wheel 26 in the first optical system. The light guide element23 also works as a splitter to partially guide the second light beampropagating toward the third lens group 27 from the second lens group 25in the second optical system. Features of the light guide element 23 aredescribed below in detail.

In FIGS. 4A, 4B, and 5, the light guide element 23 is, for example, aparallel flat plate of transparent glass or resin and has a frontsurface 23 a and a back surface 23 b, which are parallel to each other.As the light guide element 23 works as a polarization beam splitter, thefront surface 23 a has a coating that reflects the s-polarized light inthe wavelength band of the excitation light BL and transmits thep-polarized light in the wavelength band of the excitation light BL andfluorescence light YL.

In FIG. 5, the light guide element 23 includes four end surfaces: alonger-side end surface 23 c (first end surface); a longer-side endsurface 23 d (second end surface); a shorter-side end surface 23 e; anda shorter-side end surface 23 f, where the longer-side end surface 23 cand the longer-side end surface 23 d (second end surface) are a parallelpair and extending along the longer-side of the light guide element 23,and the shorter-side end surfaces 23 e and the shorter-side end surface23 f are a parallel pair and extending along the shorter-side of thelight guide element 23. The longer-side end surface 23 c, thelonger-side end surface 23 d, the shorter-side end surface 23 e, andshorter-side end surface 23 f are substantially perpendicular to each ofthe front surface 23 a and the back surface 23 b. The longer-side endsurface 23 c and the longer-side end surface 23 d are also substantiallyperpendicular to the shorter-side end surface 23 e and the shorter-sideend surface 23 f. The light guide element 23 is supported and fixed by asupport member in the vicinity of the shorter-side end surfaces 23 e and23 f outside the second light beam LF.

A direction in which the optical axis of the first lens group 22 extendsis defined as a direction M1 in FIGS. 2, 4A, and 4B. The direction M1 isperpendicular to the optical axis LX of the second optical system. Thelight guide element 23 is disposed so that the longer-side of the lightguide element 23 is tilted in a direction M2 perpendicular to thedirection M1 and the optical axis LX.

As illustrated in FIGS. 4A, 4B, and 5, the light guide element 23 isdisposed so that the front surface 23 a and the back surface 23 b aretilted by about 45 degrees with respect to the optical axis LX as viewedin the direction M2 (i.e., as viewed from the shorter-side end surface23 e and the shorter-side end surface 23 f). In the direction along theoptical axis LS, the front surface 23 a faces the phosphor wheel 26, orthe second lens group 25, and the back surface 23 b faces the colorwheel 28, or the third lens group 27.

In the light guide element 23 as viewed from the front side along theoptical axis LX, as illustrated in FIG. 5, the front surface 23 a andthe longer-side end surface 23 c face the phosphor wheel 26. The frontsurface 23 a having a larger projection area as viewed from the frontside is a first surface, and the longer-side end surface 23 c having asmaller projection area is a second surface. A first light beam isreflected toward the phosphor wheel 26 by the front surface 23 a as thefirst surface.

In the light guide element 23 as viewed from the back side along theoptical axis LX, the back surface 23 b and the longer-side end surface23 d face the color wheel 28, or the third lens group 27. A projectionarea in the back view of the back surface 23 b is larger than that ofthe longer-side end surface 23 d.

The light guide element 23 is disposed so that the optical axis LXpasses through the center of an outer shape of the light guide element23 in the front view and the back view. More specifically, in the frontview of the light guide element 23 in FIG. 5, the optical axis LX passesthrough the center of the length along the shorter-side between thelonger-side end surface 23 c and the longer-side end surface 23 d of thelight guide element 23 and the center of the length along thelonger-side between the shorter-side end surface 23 e and theshorter-side end surface 23 f of the light guide element 23. Asillustrated in FIG. 5, when a virtual plane S1 including the opticalaxis LX along the direction M1 and the virtual plane S2 including theoptical axis LX along the direction M2 are set, the configuration of thelight guide element 23 in the front view and the back view issymmetrical with respect to both the virtual plane S1 and the virtualplane S2 (i.e., the virtual plane S1 passes through the center of thelonger-side of the light guide element 30 and the virtual plane S2passes through the center of the shorter-side of the light guide element30).

In the direction M1, the length of the light guide element 23 in theshorter-side direction in the front view is entirely within the range ofthe second light beam LF. In other words, in the direction M1, both thelonger-side end surface 23 c and the longer-side end surface 23 d arewithin the range of the optical path through which the second light beamLF passes.

In the direction M2, the length of the light guide element 23 in thelonger-side direction thereof is slightly larger than the diameter ofthe second light beam LF, and a portion of each end of the light guideelement 23 around the shorter-side end surface 23 e and the shorter-sideend surface 23 f, in the longer-side direction are outside the range ofthe diameter the second light beam LF.

In other words, the front surface 23 a, the back surface 23 b, thelonger-side end surface 23 c, and the longer-side end surface 23 d ofthe light guide element 23 are disposed within the diameter of thesecond light beam LF excluding the portions of the ends of the lightguide element 23 in the direction M2 (i.e., the longer-side direction).In contrast, the shorter-side end surface 23 e and the shorter-side endsurface 23 f are disposed outside the range of the second light beam LF.

The second light beam LF including the fluorescent light YLwavelength-converted by the phosphor region 26 d of the phosphor wheel26 and the excitation light BL reflected by the excitation lightreflection region 26 e is converted from a diverging light beam into asubstantially parallel light beam by the second lens group 25 andreaches the light guide element 23. As illustrated in FIG. 5, the frontsurface 23 a and the back surface 23 b occupy a most portion of thelight guide element 23 disposed in the second light beam LF. In the mostportion of the light guide element 23, the second light beam LF directlypasses toward the third lens group 27. The longer-side end surface 23 cof the light guide element 23 is disposed at a place on which a portionof the second light beam LF from the phosphor wheel 26 is incident.

As illustrated in FIGS. 4A and 4B, a portion of the second light beam LFenters the light guide element 23 from the longer-side end surface 23 cand propagates through the light guide element 23 while repeating totalinternal reflection multiple times to exit from the longer-side endsurface 23 d. Specifically, in the light guide element 23, the lightbeam entered from the longer-side end surface 23 c is reflected multipletimes on each of the front surface 23 a and the back surface 23 b andguided to the longer-side end surface 23 d to exit. As described above,the light guide element 23 directly transmits the second light beam LFthrough the front surface 23 a and the back surface 23 b and separates aportion of the second light beam from the second light beam LF in thesecond optical system. In other words, a portion of the second lightbeam passes through the light guide element 23 in the second opticalsystem. As a result, in the second optical system, a distribution oflight quantity in the second light beam LF differs before and afterpassing through the light guide element 23.

More specifically, the light guide element 23 is arranged so that thelonger-side end surface 23 c of a light incident side is disposed on oneregion in the direction M1 direction divided by the virtual plane S2,and the longer-side end surface 23 d of a light emission side isdisposed on the other region in the M1 direction in FIG. 5. The lightguide element 23 guides a portion of the second light beam LF from theone region to the other region across the virtual plane S2.

By providing the light guide element 23 working as described above inthe second optical system, an illuminance distribution on an irradiationsurface (i.e., image display element 15) of illumination light emittedfrom the light source device 12 is changed. By appropriately arrangingthe direction and the magnitude of guiding light of the light guideelement 23, the illuminance distribution on the irradiation surface(i.e., image display element 15) improves.

The light guide element 23 reflects the first light beam emitted fromthe laser light source group 20 in the first optical system toward thephosphor wheel 26 and partially separates the second light beam in thesecond optical system. The light guide element 23 works in both thefirst optical system and the second optical system, which makes theoptical system simple (i.e., simple configuration). The illuminancedistribution improves with the simple configuration having less opticalelements.

A portion of the second light beam LF by the light guide element 23 isguided within the optical path of the second optical system (inside thediameter of the second light beam LF). As a result, loss of the lightquantity caused by guiding light in the light guide element 23 stops andthe illuminance distribution improves without decreasing the light useefficiency in the light source device 12.

In addition, the illuminance distribution can substantially be changedby repeating the total internal reflection multi times while guidinglight inside the light guide element 23

As illustrated in FIG. 5, the light guide element 23 has the length ofthe diameter of the second light beam LF in the longer-side direction.This configuration enables the entirety of the second light beam LF inthe longer-side direction (i.e., the direction M2) of the light guideelement 23 to undergo the adjustment of the illuminance distribution bythe light guide element 23.

In the projector 10, there is a correlation between the illuminancedistribution of illumination light at the image display element 15 andthe illuminance distribution on the screen 17. To prevent changes in theilluminance distribution due to other factors such as the action of theprojection optical system 16, the light guide element 32 is arranged toseparate (pass) light as appropriate in the second optical system. Thisimproves the light distribution of the light source device 12, or theprojector 10, thus advantageously reducing the unevenness of thedistribution of illuminance on the screen 17.

FIG. 6 is an illustration of the results of the experiments andmeasurements demonstrating reduction in the unevenness of theilluminance distribution by the light guide element 23. In FIG. 6, thegraph of the “example” is an illuminance distribution on the screen 17obtained by an experiment using the light guide element 23 thatseparated (guided) a portion of the second light beam from the secondlight beam LF and the graph of “comparative example” is an illuminancedistribution on the screen 17 obtained by an experiment without guidinglight by the light guide element 23. In the example, the longer-side endsurface 23 c and the longer-side end surface 23 d of the light guideelement 23 were configured to transmit light (i.e., transmissionsurface), and the light entered the light guide element 23 from thelonger-side end surface 23 c and exited from the longer-side end surface23 d of the light guide element 23. In the comparative example, thelonger-side end surface 23 c and the longer-side end surface 23 d of thelight guide element 23 were configured to absorb light (i.e., absorptionsurface), and the light did not enter the light guide element 23 fromthe longer-side end surface 23 c and did not exit from the longer-sideend surface 23 d of the light guide element 23. When a full-on image(i.e., all pixels in the image display element 15 are on) was projectedonto the screen 17 under the same condition excluding the differencebetween the transmission surface and the absorption surface describedabove, the illuminance distribution illustrated in FIG. 6 was obtained.

As illustrated in FIG. 6, an unevenness of an illuminance distributionin the example is smaller than that of comparative example, and theunevenness of the illuminance distribution on the screen 17 improves. Inparticular, in an area from the center to the upper left portion of thescreen 17 of the comparative example in FIG. 6, the unevenness of theilluminance distribution is lager (i.e., an area of lower illuminancespreads). In contrast, in the example, the unevenness of the illuminancedistribution is advantageously reduced (i.e., an area of higherilluminance spreads).

As an example, evaluation of the illuminance distribution on the screen17 is described below. The illuminance on the screen 17 is normalized asthe maximum value in the illuminance distribution on the screen is 100%.An image projection area on the screen 17 projected by the projector 10is equally divided into nine rectangular regions, and an average ofilluminance is calculated for each region. In addition, an average ofthe illuminance of the nine regions is calculated. By referring to theaverage calculated in this manner, the unevenness of the illuminancedistribution on the screen 17 is quantitatively evaluated.

In FIG. 6, Table 1 represents the average of the illuminance of each ofthe nine regions on the screen 17 in the example, and Table 2 representsthe average of the illuminance of each of the nine regions on the screen17 in the comparative example. The averages of the illuminancecalculated based on the values of Tables 1 and 2 are 88.0% in theexample and 86.9% in the comparative example, and the unevenness of theilluminance distribution on the screen 17 reduces in the example ascompared with the comparative example.

In the present embodiment, an angle formed by the normal line of thesecond surface (the longer-side end surface 23 c) of the light guideelement 23 and the optical axis LX of the second optical system is 45degrees, an average W₃ of a length of the second surface (thelonger-side end surface 23 c) in a direction perpendicular to the ridgeline formed by the first surface (the longer-side end surface 23 c) andthe second surface (the longer-side end surface 23 c) of the light guideelement 23 is 0.9 mm, and the diameter ϕ_(L) of the second light beam LFat a position of the ridge line formed by the first surface (the frontsurface 23 a) and the second surface (the longer-side end surface 23 c)of the light guide element 23 of the second optical system is 20 mm. Thediameter ϕ_(L) of the second light beam LF is a value (light beamdiameter) of the second light beam LF in a plane perpendicular to theoptical axis LX at the end of the light guide element 23 at the side ofthe phosphor wheel 26 (wavelength conversion element). When projectedonto a plane perpendicular to the optical axis of the second opticalsystem, the light guide element 23 has the following dimensions: W₂(average length) is an average of the length of the second surface in adirection perpendicular to a ridge line formed by the first surface andthe second surface, ϕ_(L) is the diameter of the second light beam on anoptical surface immediately before the light guide element 23 in thesecond optical system, H_(i) is distance between the optical axis LX ofthe second optical system and the center of the longer-side end surface23 c of a light incident side, and H_(o) is distance between an opticalaxis LX of the second optical system and the center of the longer-sideend surface 23 d of a light emission side. Specific values for W₂,ϕ_(L), H_(i), and H_(o) are below:

W₂=0.64 mm;

ϕ_(L)=20 mm;

H_(i)=7.07 mm; and

H_(o)=7.07 mm.

From W₂ and ϕ_(L) described above, W₂/ϕ_(L) is 0.032.

The ratio of W₂ to ϕ_(L) (W₂/ϕ_(L)) is a gauge of the light quantityguided by the light guide element 23. Preferably, a conditionalexpression (1) below is satisfied.

$\begin{matrix}{{{0.0}18} < {W_{2}/\phi_{L}} < {{0.0}35}} & (1)\end{matrix}$

When W₂/ϕ_(L) of the conditional expression (1) is less than 0.018, thelight quantity guided by the light guide element 32 is insufficient toobtain the effect of adjusting the illuminance distribution. WhenW₂/ϕ_(L) of the conditional expression (1) is larger than 0.032, thelight quantity guided by the light guide element is excessively largerand difficult to adjust the illuminance distribution properly.

More preferably, a conditional expression (2) below is satisfied.

$\begin{matrix}{{{0.0}22} < {W_{2}/\phi_{L}} < {{0.0}33}} & (2)\end{matrix}$

The illuminance distribution on the screen 17 may be evaluated by amethod different from the method described above. For example, thenumber of regions on the screen 17 for obtaining the average of theilluminance distribution may be other than nine. In addition, the shapeof each region on the screen 17 may be other than the rectangle equallydivided.

FIG. 7 is an illustration of the light source device 12 according to thesecond embodiment. The light source device 12 of the second embodimentincludes a light guide element 30 instead of the light guide element 23according to the first embodiment.

In the propagation direction (the direction M1) of the first light beamemitted from the laser light source group 20 toward the light guideelement 30, the light guide element 30 is offset from the optical axisLX (i.e., offset configuration) in FIG. 8. The light guide element 30 isa dichroic mirror, instead of a polarization beam splitter such as thelight guide element 23, that reflects light in the wavelength band ofthe excitation light BL and transmits light in the wavelength band ofthe fluorescence light YL. There is no quarter-wave plate between thelight guide element 30 and the second lens group 25 (i.e., nonquarter-wave plate configuration). The second embodiment differs fromthe first embodiment in the offset configuration, the dichroic mirror,and non quarter-wave plate configuration. Other portions of theconfiguration are the same as those of the light source device 12according to the second embodiment. Hereinafter, in descriptions on thesecond embodiment, the common descriptions between the first and thesecond embodiments are omitted.

The light guide element 30 is, for example, a parallel flat plate of atransparent material such as glass or plastic and has a front surface 30a and a back surface 30 b parallel to each other. The front surface 30 aof the light guide element 30 has a coating that reflects light in thewavelength band of the excitation light BL and transmits light in thewavelength band of the fluorescence light YL so that the light guideelement 30 works as a dichroic mirror.

As illustrated in FIG. 9, when a virtual plane S1 including the opticalaxis LX along the M1 direction and the virtual plane S2 including theoptical axis LX along the direction M2 are set, the configuration of thelight guide element 30 as viewed from the front and back sides along theoptical axis LX is symmetrical with respect to the virtual plane S1(i.e., the virtual plane S1 passes through the center of longer-side ofthe light guide element 30). On the other hand, the light guide element30 as viewed from the front and back sides does not intersect with thevirtual plane S2 and is offset from the optical axis LX in the directionM1.

The first light beam emitted from the laser light source group 20 entersthe phosphor wheel 26 through the first optical system from the firstlens group 22 to the second lens group 25. In addition, the second lightbeam having the wavelength converted by the phosphor wheel 26 (i.e., thesecond light beam wavelength-converted from the first light beam by thewavelength conversion element) enters the color wheel 28 through thesecond optical system from the second lens group 25 to the third lensgroup 27. The fluorescent light YL passes through the light guideelement 30 in a region in which the light guide element 30 is disposedin the second optical system, and the fluorescent light YL and theexcitation light BL pass through a region in which the light guideelement 30 is not disposed in the second optical system and reach thecolor wheel 28. Since the light guide element 30 is offset from theoptical axis LX in the M1 direction, the excitation light BL can passthrough a wider region including the vicinity of the optical axis LX inthe second optical system.

As illustrated in FIGS. 8 and 9, the light guide element 30 includesfour end surfaces: a longer-side end surface 30 c (a first end surface);a longer-side end surface 30 d (a second end surface); a shorter-sideend surface 30 e; and a shorter-side end surface 30 f, where thelonger-side end surface 30 c and the longer-side end surface 30 d are aparallel pair and extending along the longer-side of the light guideelement 30, and the shorter-side end surface 30 e and the shorter-sideend surface 30 f are a parallel pair and are extending along theshorter-side of the light guide element 30. The longer-side end surface30 c, the longer-side end surface 30 d, the shorter-side end surface 30e, and shorter-side end surface 30 f are substantially perpendicular tothe front surface 30 a and the back surface 30 b. The longer-side endsurface 30 c and the longer-side end surface 30 d are also substantiallyperpendicular to the shorter-side end surface 30 e and the shorter-sideend surface 30 f. The light guide element 30 is supported and fixed by asupport member in the vicinity of the shorter-side end surface 30 e andthe shorter-side end surface 30 f at outside the second light beam LF.

As illustrated in FIG. 8, the light guide element 30 is disposed so thatthe front surface 30 a and the back surface 30 b are tilted by about 45degrees with respect to the optical axis LX as viewed in the directionM2 (i.e., as viewed from the shorter-side end surface 30 e and theshorter-side end surface 30 f). In the direction along the optical axisLX, the front surface 30 a faces the phosphor wheel 26, or the secondlens group 25, and the back surface 30 b faces the color wheel 28, orthe third lens group 27.

In the light guide element 30 as viewed from the front side along theoptical axis LX, as illustrated in FIG. 9, the front surface 30 a andthe longer-side end surface 30 c face the phosphor wheel 26. The frontsurface 30 a having a larger projection area as viewed from the frontside is a first surface, and the longer-side end surface 30 c having asmaller projection area is a second surface. A first light beam isreflected toward the phosphor wheel 26 by the front surface 30 a as thefirst surface.

In the light guide element 30 as viewed from the back side along theoptical axis LX, the back surface 30 b and the longer-side end surface30 d face the color wheel 28, and the third lens group 27. A projectionarea of the back surface 30 b is larger than that of the longer-side endsurface 30 d as viewed from the back side.

In the direction M1, the length of the light guide element 30 in theshorter-side direction as viewed from the front side is entirely withinthe range of the second light beam LF. In other words, in the directionM1, both the longer-side end surface 30 c and the longer-side endsurface 30 d are within the range of the optical path through which thesecond light beam LF passes.

In the direction M2, the length of the light guide element 30 in thelonger-side direction thereof is slightly larger than the diameter ofthe second light beam LF, and portions of each end of the light guideelement 30 around the longer-side end surface 30 c and the longer-sideend surface 30 d, in the longer-side direction are outside the range ofthe second light beam LF.

In other words, the front surface 30 a, the back surface 30 b, thelonger-side end surface 30 c, and the longer-side end surface 30 d ofthe light guide element 30 are disposed within the diameter of thesecond light beam LF excluding the portions of the ends of the lightguide element 30 in the direction M2 (i.e., the longer-side direction).In contrast, the shorter-side end surface 30 e and the shorter-side endsurface 30 f are disposed outside the range of the second light beam LF.

As illustrated in FIG. 8, a portion of the second light beam LF entersthe light guide element 30 from the longer-side end surface 30 c andpropagates through the light guide element 30 while repeating totalinternal reflection multiple times to exit from the longer-side endsurface 30 d. The light guide element 30 separates a portion of thesecond light beam from the second light beam LF in the second opticalsystem. In other words, a portion of the second light beam passesthrough the light guide element 30. As a result, in the second opticalsystem, the distribution of light quantity in the second light beam LFdiffers before and after the light guide element 30.

Unlike the light guide element 23 according to the first embodiment, thelight guide element 30 is arranged to offset in the direction M1 withoutintersecting the optical axis LX. The longer-side end surface 30 c onwhich a portion of the second light beam LF is incident is disposed inthe vicinity of a peripheral portion of the second light beam LF. Inaddition, the longer-side end surface 30 d from which the light thatpropagates in the light guide element 30 is emitted is disposed in thevicinity of the center close to the optical axis LX. The light guideelement 30 works to bring a portion of the second light beam LF passingthrough a peripheral portion of the light guide element 30 closer to theoptical axis LX in the direction M1. In other words, the light guideelement 30 in the second optical system has a function to adjust theilluminance distribution to brighten the vicinity of the center of theimage display element 15 and the screen 17.

The light guide element 30 has the length of the diameter of the secondlight beam LF. This configuration enables the entirely of the secondlight beam LF in the longer-side direction (i.e., the direction M2) ofthe light guide element 30 to undergo adjustment of the illuminancedistribution by the light guide element 30.

FIG. 10 is an illustration of the results of the experiments andmeasurements demonstrating reduction in the unevenness of theilluminance distribution by the light guide element 30. In FIG. 10, thegraph of the “example” is an illuminance distribution on the screen 17obtained by an experiment using the light guide element 30 thatseparated (guided) a portion of the second light beam from the secondlight beam LF and the graph of “comparative example” is an illuminancedistribution on the screen 17 obtained by an experiment without guidinglight by the light guide element 30. In the example, the longer-side endsurface 30 c and the longer-side end surface 30 d of the light guideelement 30 were configured to transmit light (i.e., transmissionsurface), and the light entered the light guide element 30 from thelonger-side end surface 30 c and exited from the longer-side end surface30 d of the light guide element 30. In the comparative example, thelonger-side end surface 30 c and the longer-side end surface 30 d of thelight guide element 30 were configured to absorb light (i.e., absorptionsurface), and the light did not enter the light guide element 30 fromthe longer-side end surface 30 c and did not exit from the longer-sideend surface 30 d of the light guide element 30. When a full-on image(i.e., all pixels in the image display element 15 are on) was projectedonto the screen 17 under the same conditions condition excluding thedifference between the transmission surface and the absorption surfacedescribed above, the illuminance distribution illustrated in FIG. 10 wasobtained.

As illustrated in FIG. 10, an unevenness of an illuminance distributionin the example is smaller than that in the comparative example, and theunevenness of illuminance distribution on the screen 17 reduces. Inparticular, in an area from the center close to the upper of the screen17 in FIG. 10, the unevenness of the illuminance distribution of theexample is smaller than that of the comparative example.

The unevenness of the illuminance distribution on the screen 17 wasevaluated according to the same evaluation criteria as in the firstembodiment. In FIG. 10, Table 3 represents the average of theilluminance of each of the nine regions on the screen 17 in the example,and Table 4 represents the average of the illuminance of each of thenine regions on the screen 17 in the comparative example. In the secondembodiment, the averages of the illuminance calculated based on thevalues of Tables 3 and 4 are 90.8% in the example and 90.0% in thecomparative example. Thus, the unevenness of illuminance distribution onthe screen 17 reduces in the example as compared with the comparativeexample.

In the present embodiment, the angle formed by the normal line of thesecond surface (the longer-side end surface 30 c) of the light guideelement 30 and the optical axis LX of the second optical system is 45degrees, an average W₃ of a length of the second surface (thelonger-side end surface 30 c) in a direction perpendicular to the ridgeline formed by the first surface (the longer-side end surface 30 c) andthe second surface (the longer-side end surface 30 c) of the light guideelement 30 is 0.7 mm, and the diameter ϕ_(L) of the second light beam LFat the position of the ridge line formed by the first surface (the frontsurface 30 a) and the second surface (the longer-side end surface 30 c)of the light guide element 30 of the second optical system is 20 mm. Thediameter ϕ_(L) of the second light beam LF is a value (light beamdiameter) of the second light beam LF in a plane perpendicular to theoptical axis LX at the end of the light guide element 30 at a side ofthe phosphor wheel 26 (the wavelength conversion element).

Specific values for W₂, ϕ_(L), H_(i), and H_(o) are below:

W₂=0.49 mm;

ϕ_(L)=20 mm;

H_(i)=8.04 mm; and

H_(o)=0.96 mm.

Thus, the ratio of W₂ to ϕ_(L) (W₂/ϕ_(L)) is 0.025, which satisfiesconditional expressions (1) and (2).

In the light source device 12 according to the third embodiment, aconfiguration of the light guide element 31 as viewed from the front andthe back sides along the optical axis LX is illustrated in FIG. 11. Inthe third embodiment, the configuration excluding the light guideelement 31 is the same as the configuration of the second embodiment, inwhich the common descriptions of the third embodiment and the secondembodiment are omitted.

The light guide element 31 is, for example a parallel flat plate oftransparent material such as glass or resin, and a front surface 31 a, aback surface 31 b, a longer-side end surface 31 c (a first end surface),a longer-side end surface 31 d (a second end surface), a shorter-sideend surface 31 e, and a shorter-side end surface 31 f are correspondingto the front surface 30 a, the back surface 30 b, the longer-side endsurface 30 c (the first end surface), the longer-side end surface 30 d(the second end surface), the shorter-side end surface 30 e, and theshorter-side end surface 30 f of the light guide element 30 according tothe second embodiment.

The configuration of the light guide element 31 is asymmetrical withrespect to both the virtual plane S1 including the optical axis LX alongthe direction M1 and the virtual plane S2 including the optical axis LXalong the direction M2. More specifically, the light guide element 31 isoffset from the optical axis LX in the direction M1, which is the sameas the light guide element 30 of the second embodiment and does notintersect with the virtual plane S2. Furthermore, in the light guideelement 31, the shorter-side end surface 31 e is offset so that theshorter-side end surface 31 e is closer to the virtual plane S1 than theshorter-side end surface 31 f. As a result, the shorter-side end surface31 e is disposed within the diameter of the second light beam LF. Inother words, the configuration of the light guide element 31 isasymmetrical with respect to the virtual planes S1 and S2, the directionM1 and the direction M2, and the optical axis LX. In the direction M2,the light guide element 31 is divided into two portions: one portion isdisposed within the second light beam LF and light is guided; and theother portion is disposed outside the second light beam LF and light isnot guided. The light guide element 31 is supported and fixed by asupport member in the vicinity of the shorter-side end surfaces 31 fdisposed outside the second light beam LF.

The virtual plane S1 includes the optical axis LX of the second opticalsystem and the light beams before and after passing through the lightguide element 31 (i.e., it is longitudinally across both the longer-sideend surface 31 c and the longer-side end surface 31 d). Since theconfiguration of the light guide element 31 is asymmetrical with respectto the virtual plane S1 and the optical axis LX in the direction M2, alatitude of adjusting the illumination distribution on the image displayelement 15 and the screen 17 increases.

Although the configuration of the light guide element 31 illustrated inFIG. 11 is asymmetrical with respect to both the virtual plane S1 andthe virtual plane S2, a configuration of the light guide element 31 maybe symmetrical with respect to the virtual plane S2 and asymmetricalwith respect to the virtual plane S1.

FIG. 12 is a schematic view of a configuration of a light source device12 according to the fourth embodiment. The light source device 12 of thefourth embodiment is different from that of the third embodiment in theconfiguration of the light guide element 32. In the fourth embodiment,the configuration excluding the light guide element 32 is the same asthe configuration of the third embodiment. Hereinafter, in descriptionson the fourth embodiment, the common descriptions between the third andthe fourth embodiments are omitted.

FIGS. 13 and 14 are schematic views of a configuration of the lightguide element 32 according to the fourth embodiment. A front surface 32a, a back surface 32 b, a longer-side end surface 32 c, a longer-sideend surface 32 d, a shorter-side end surface 32 e, and a shorter-sideend surface 32 f of the light guide element 32 illustrated in FIGS. 13and 14 are corresponding to the front surface 31 a, the back surface 31b, the longer-side end surface 31 c (the first end surface), thelonger-side end surface 31 d (the second end surface), the shorter-sideend surface 31 e, and the shorter-side end surface 31 f of the lightguide element 31. The fourth embodiment is different from the thirdembodiment in a configuration of the light guide element 32. In theconfiguration of the light guide element 32 according to the fourthembodiment, the light guide element 32 is disposed in a place closer tothe first optical system and farther from the second virtual surface S2including the optical axis LX along the direction M2. Other portions ofthe configuration are the same as those of the light source device 12according to the third embodiment. Hereinafter, in a description on thefourth embodiment, the common descriptions between the third and thefourth embodiments are omitted. The light guide element 32 is supportedand fixed by a support member in the vicinity of the shorter-side endsurfaces 32 f disposed outside the second light beam LF.

As illustrated in FIG. 13, a portion of the second light beam LF entersthe light guide element 32 from the longer-side end surface 32 c andpropagates through the light guide element 32 while repeating totalinternal reflection multiple times to exit from the longer-side endsurface 32 d. The light guide element 32 separates a portion of thesecond light beam from the second light beam LF in the second opticalsystem. In other words, a portion of the second light beam passesthrough the light guide element 30. As a result, in the second opticalsystem, the distribution of the light quantity in the second light beamLF differs before and after the light guide element 32.

As illustrated in FIG. 13, in the light guide element 32, thelonger-side end surface 32 c on which a portion of the second light beamLF is incident is disposed on the side of the center close to theoptical axis LX. In addition, the longer-side end surface 32 d to emitlight that propagates in the light guide element 32 is disposed in thevicinity of a peripheral portion of the second light beam LF. The lightguide element 32 works to keep away a portion of the of the second lightbeam LF in the vicinity of the center of the second light beam LF fromthe optical axis LX in the direction M1. In other words, the light guideelement 32 in the second optical system has an effect to adjust theilluminance distribution to brighten the vicinity of the periphery ofthe image display element 15 and the screen 17.

FIG. 15 is an illustration of the results of experiments andmeasurements demonstrating reduction in the unevenness of theilluminance distribution by the light guide element 32 according to thefourth embodiment. In FIG. 15, the graph of the “example” is anilluminance distribution on the screen 17 obtained by an experimentusing the light guide element 32 that separated (guided) a portion ofthe second light beam from the second light beam LF and the graph of“comparative example” is an illuminance distribution on the screen 17obtained by an experiment without guiding light by the light guideelement 32. In the example, the longer-side end surface 32 c and thelonger-side end surface 32 d of the light guide element 32 wereconfigured to transmit light (i.e., transmission surface), and the lightentered the light guide element 32 from the longer-side end surface 32 cand exited from the longer-side end surface 32 d of the light guideelement 32. In the comparative example, the longer-side end surface 32 cand the longer-side end surface 32 d of the light guide element 32 wereconfigured to absorb light (i.e., absorption surface), and the light didnot enter the light guide element 32 from the longer-side end surface 32c and did not exit from the longer-side end surface 32 d of the lightguide element 32. When a full-on image (i.e., all pixels in the imagedisplay element 15 are on) was projected onto the screen 17 under thesame conditions condition excluding the difference between thetransmission surface and the absorption surface described above, theilluminance distribution illustrated in FIG. 15 was obtained.

As illustrated in FIG. 15, an unevenness of an illuminance distributionin the example is smaller than that in the comparative example, and theunevenness of illuminance distribution on the screen 17 reduces. Inparticular, in an area from the center close to the upper of the screen17 in FIG. 15, the unevenness of the illuminance distribution of theexample is smaller than that of the comparative example.

The unevenness of illuminance on the screen 17 was evaluated accordingto the same evaluation criteria as in the first embodiment. In FIG. 15,Table 5 represents the average of the illuminance of each of the nineregions on the screen 17 in the example, and Table 6 represents theaverage of the illuminance of each of the nine regions on the screen 17in the comparative example. In the fourth embodiment, the averages ofthe illuminance calculated based on the values of Tables 5 and 6 is89.4% in the example and 89.1% in the comparative example. Thus, theunevenness of the illuminance distribution on the screen 17 reduces inthe example as compared with the comparative example.

In the present embodiment, an angle formed by the normal line of thesecond surface (the longer-side end surface 32 c) of the light guideelement 32 and the optical path LX of the second optical system is 45degrees, an average W₃ of a length of the second surface (thelonger-side end surface 32 c) in a direction perpendicular to the ridgeline formed by the first surface (the front surface 32 a) and the secondsurface (the longer-side end surface 32 c) of the light guide element 32is 0.7 mm, and the diameter ϕ_(L) of the second light beam LF at theposition of the ridge line formed by the first surface (the frontsurface 32 a) and the second surface (the longer-side end surface 32 c)of the light guide element 32 of the second optical system is 21 mm. Thediameter ϕ_(L) of the second light beam LF is a value on a planeperpendicular to the optical axis LX at the end of the light guideelement 32 at a side of the phosphor wheel 26 (the wavelength conversionelement).

Specific values for W₂, ϕ_(L), H_(i), and H_(o) are below:

W₂=0.49 mm;

ϕ_(L)=21 mm;

H_(i)=0.96 mm; and

H_(o)=8.04 mm.

The ratio of W₂ to ϕ_(L) (W₂/ϕ_(L)) is 0.024, which satisfies theconditional expressions (1) and (2).

The ratio of H_(i) to ϕ_(L) (H_(i)/ϕ_(L)) is 0.046.

The ratio of H_(i) to ϕ_(L) (H_(i)/ϕ_(L)) is an index indicating apositional ratio of a portion of light separated by the light guideelement in the second light beam to the diameter of the second lightbeam. In a case where light is guided by the light guide element so asto be farther from the optical axis. Preferably, a conditionalexpression (3) below is satisfied.

$\begin{matrix}{{H_{i}/\phi_{L}} < {0.1}} & (3)\end{matrix}$

In general, since light quantity is larger in the vicinity of theoptical axis LX in the second light beam LF, a way of guiding light fromthe vicinity of the center of optical axis LX to the vicinity of theperipheral of the optical axis by the light guide element is effectiveto adjust to reduce the unevenness of the illuminance distribution. Whenthe ratio of H_(i) to ϕ_(L) (H_(i)/ϕ_(L)) is larger than 0.1, the lightguided by the light guide element is farther from the vicinity of theoptical axis LX, and the unevenness of the illuminance distribution isdifficult to reduce.

In the configuration of the light guide element 32 according to thefourth embodiment, the light in the vicinity of the center of the secondlight beam LF (i.e., a portion of the second light beam LF closer to theoptical axis LX) is guided to a peripheral portion of the second lightbeam LF (i.e., a portion of the second light beam farther from theoptical axis LX). When the light quantity in the vicinity of the centerof the second light beam LF is larger, the configuration of the lightguide element 32 according to the fourth embodiment is effective toadjust the light quantity in the second light beam LF. As a result, theilluminance distribution of the image display element 15 and the screen17 is uniformized.

FIG. 16 is a schematic view of a configuration of the light sourcedevice 12 according to the fifth embodiment. In the light source device12 according to the fifth embodiment, an arrangement of the light guideelement 33 guides a center portion of light (i.e., a portion closer tothe optical axis LX) in the second light beam LF to a peripheral portion(i.e., a portion farther from the optical axis LX). In the fourthembodiment, the light guide element 32 also guides a center portion oflight in the second light beam LF to a peripheral portion. A frontsurface 33 a, a back surface 33 b, a longer-side end surface 33 c, and alonger-side end surface 33 d of the light guide element 33 arecorresponding to the front surface 32 a, the back surface 32 b, thelonger-side end surface 32 c (the first end surface), and thelonger-side end surface 32 d (the second end surface) of the light guideelement 32 (FIG. 13) according to the fourth embodiment.

In the fifth embodiment, an angle formed by the optical axis LX and anormal line of the second surface (the longer-side end surface 33 c) ofthe light guide element 33 is 35 degrees, and the optical axis of thefirst optical system tilts by 20 degrees so that the first light beamreflected by the first surface (the front surface 33 a) of the lightguide element 33 hits the wavelength conversion element (the phosphorwheel 26), that is, the incident angle on the first surface (the frontsurface 33 a) of the light guide element 33 is 55 degrees, which isdifferent from the fourth embodiment. The normal line of the secondsurface (the longer-side end surface 33 c) of the light guide element 33is closer to the direction of the optical axis LX of the second opticalsystem than the normal line of the second surface of the light guideelement 32 according to the fourth embodiment. The normal line of thefirst surface (the front surface 33 a) of the light guide element 33 isfarther from the direction of the optical axis LX of the second opticalsystem. The angle formed by the normal line of the second surface (thelonger-side end surface 33 c) and the optical axis LX of the secondoptical system is 35 degrees, and an angle formed by the normal line ofthe first surface (the front surface 33 a) and the second optical axisLX is 55 degrees. The angle formed by the normal line of the secondsurface (the longer-side end surface 33 c) and the optical axis LX ofthe second optical system is smaller than the angle formed by the normalline of the first surface (the front surface 33 a) and the optical axisLX of the second optical system. Other portions of the configurationaccording to the fifth embodiment are the same as those of the lightsource device 12 according to the fourth embodiment. Hereinafter, indescriptions on the fifth embodiment, the common descriptions betweenthe fourth and the fifth embodiments are omitted.

As illustrated in FIG. 16, the laser light source group 20, thecollimator lens group 21, and the first lens group 22 are configured tomatch the configuration of the light guide element 33. The excitationlight BL emitted from the first lens group 22 is reflected by the firstsurface (the front surface 33 a) of the light guide element 33 andenters the second lens group 25 along the optical axis LX.

In the light source device 12 according to the fifth embodiment: theangle formed by the normal line of the second surface (the longer-sideend surface 33 c) of the light guide element 33 and the optical axis LXis 35 degrees; the average length W₃ of the second surface (thelonger-side end surface 33 c) in a direction perpendicular to the ridgeline formed by the first surface (the longer-side end surface 33 c) andthe second surface (the longer-side end surface 33 c) of the light guideelement 33 is 0.7 mm; and diameter ϕ_(L) of the second light beam LF atthe position of the ridge line formed by the first surface and thesecond surface (the longer-side end surface 33 c) is 20 mm. The diameterϕ_(L) of the second light beam LF is a value on a plane perpendicular tothe optical axis LX at the end of the light guide element 33 at a sideof the phosphor wheel 26 (the wavelength conversion element).

Specific values for W₂, ϕ_(L), H_(i), and H_(o) are below:

W₂=0.57 mm;

ϕ_(L)=20 mm;

H_(i)=1.63 mm; and

H_(o)=7.37 mm.

Thus, the ratio of W₂ to ϕ_(L ()W₂/ϕ_(L)) is 0.029, which satisfies theconditional expressions (1) and (2).

The ratio H_(i) to ϕ_(L) (H_(i)/ϕ_(L)) is 0.082, which satisfies theconditional expression (3). In the light source device 12 according tothe fifth embodiment, the angle formed by the normal line of the secondsurface (the longer-side end surface 33 c) of the light guide element 33and the optical axis LX of the second optical system is smaller than theangle formed by the normal line of the first surface (the front surface33 a) and the optical axis LX of the second optical system, so that thelight quantity incident on the second surface (the longer-side endsurface 33 c) and guided by the light guide element 33 can be increased.Thus, the ratio of W₂ to ϕ_(L) (W₂/ϕ_(L)) increases. In the light sourcedevice 12 according to the fifth embodiment, the light guide element 33can efficiently adjust the distribution of light quantity of the lightbeam LF.

In each of the embodiments described above, the longer-side end surface23 c (30 c, 31 c, 32 c, 33 c) and the longer-side end surface 23 d (30d, 31 d, 32 d, 33 d) of the light guide element 23 (30, 31, 32, 33) areparallel to each other (i.e., parallel configuration). The parallelconfiguration is preferable because the directions of incidence andemission of light separated by the light guide element 23 (30, 31, 32,33) in the second optical system align. In one or more embodiments, afirst end surface corresponding to the longer-side end surface 23 c (30c, 31 c, 32 c, 33 c) and a second end surface corresponding to thelonger-side end surface 23 d (30 d, 31 d, 32 d, 33 d) may benon-parallel.

In each of the embodiments described above, the longer-side end surface23 c (30 c, 31 c, 32 c, 33 c) and the longer-side end surface 23 d (30d, 31 d, 32 d, 33 d) of the light guide element 23 (30, 31, 32, 33) areperpendicular to the front surface 23 a (30 a, 31 a, 32 a, 33 a) and theback surface 23 b (30 b, 31 b, 32 b, 33 b). In the first to fourthembodiments, the longer-side end surface 23c (30 c, 31 c, 32 c) and thelonger-side end surface 23 d (30 d, 31 d, 32 d) tilt by about 45 degreeswith respect to the optical axis LX of the second optical system. In oneor more embodiments, the angle of the first end surface or the secondend surface of the light guide element with respect to the optical axisLX may be other than 45 degrees. For example, as in the fifthembodiment, by setting the angle of the first end surface or the secondend surface with respect to the optical axis LX to be larger than 45degrees (to be angled), the projection area in a view along the opticalaxis LX increases, and the proportion of the second light beam LFpassing through the light guide element is increased.

The present invention is particularly useful in an image displayapparatus (projector) that projects an image onto a projection surface.Moreover, the present invention can also apply to apparatuses or devicesother than the image display apparatuses as long as an illuminancedistribution is required to improve. The present invention can alsoapply to an optical system other than a projection optical system, forexample, a light source optical system, a light source unit, or a lightsource device. In the light source optical system, the light sourceunit, and the light source device of the present invention, lightemitted from the light source may be used in applications other thanimage projection.

Each of the embodiments described above is an application of aprojector, and the illuminance distribution on the screen on which animage is projected by the projector is used as an evaluation referenceas illustrated in FIGS. 6 and 10. However, the illuminance distributionmay be evaluated at a place other than the screen to measure animprovement in the illuminance distribution. For example, the lightsource optical system, the light source unit, or the light source devicecan also be evaluated by measuring the illuminance distribution on theimage display element 15 (i.e., a surface irradiated with the light fromthe light source device 12) in the embodiments described above.

Although the light source device 12 of the embodiment described aboveemits light of multiple colors in a time-division manner, the lightsource device or the light source unit of the present invention is notlimited to a light source device or a light source unit that emits lightof multiple colors in a time-division manner.

Although the present invention has been described with reference to theembodiments and the modifications based on the accompanying drawings,the present invention is not limited to the embodiments described aboveand modifications, and various modifications and applications can bemade without departing from the scope of the present invention.

In the embodiment described above, the configuration and the likeillustrated in the accompanying drawings are not limited thereto, andcan be appropriately changed within a range in which the effects of thepresent invention are exhibited. In addition, the present invention canbe implemented with appropriate modifications without departing from thespirit of the present invention. The above-described embodiments areillustrative and do not limit the present invention. Thus, numerousadditional modifications and variations are possible in light of theabove teachings. For example, elements and/or features of differentillustrative embodiments may be combined with each other and/orsubstituted for each other within the scope of the present invention.

1. A light source optical system comprising: a first optical systemconfigured to guide a first light beam having a first wavelength emittedfrom a light source to a wavelength conversion element; the wavelengthconversion element configured to convert the first light beam into asecond light beam having a second wavelength different from the firstwavelength, and emit the second light beam; and a second optical systemthrough which the second light beam emitted from the light conversionelement passes, the second optical system including a light guideelement configured to guide a portion of the second light beam from oneend surface of the light guide element to the other end surface of thelight guide element to separate the portion of the second light beamfrom the second light beam.
 2. The light source optical system accordingto claim 1, wherein the light guide element has: a first surface; and asecond surface that the portion of the second light beam enters, whereina projection area of the second surface is smaller than that of thefirst surface, the projection area on a plane perpendicular to anoptical axis of the second optical system.
 3. The light source opticalsystem according to claim 2, wherein a conditional expression below issatisfied: 0.018<W₂/ϕ_(L)<0.035 where, on the plane perpendicular to theoptical axis of the second optical system, W₂ is an average length ofthe second surface in a direction perpendicular to a ridge line betweenthe first surface and the second surface in a projection of the lightguide element onto the plane, and ϕ_(L) is a diameter of the secondlight beam at one end of the light guide element closer to thewavelength conversion element along the optical axis.
 4. The lightsource optical system according to claim 2, wherein the first surface ofthe light guide element reflects the first light beam toward thewavelength conversion element.
 5. The light source optical systemaccording to claim 2, wherein an angle between a normal line of thesecond surface and the optical axis of the second optical system issmaller than an angle between a normal line of the first surface and theoptical axis of the second optical system.
 6. The light source opticalsystem according to claim 1, wherein the light guide element isconfigured to allow the portion of the second light beam to repeat totalinternal reflection multiple times in the light guide element and exitfrom the light guide element.
 7. The light source optical systemaccording to claim 1, wherein the light guide element is a parallel flatplate having a first end surface and a second end surface, andconfigured to allow the portion of the second light beam to enter thefirst end surface and exit from the second end surface.
 8. The lightsource optical system according to claim 7, wherein the light guideelement is asymmetrically arranged with respect to an optical axis ofthe second optical system in a direction in which the first end surfaceand the second end surface extend.
 9. The light source optical systemaccording to claim 1, wherein the light guide element is disposedintersecting with an optical axis of the second optical system to guidethe portion of the second light beam from a region to another regionacross a plane including the optical axis of the second optical system.10. The light source optical system according to claim 1, wherein thelight guide element is configured to guide the portion of the secondlight beam to be closer to an optical axis of the second optical system.11. The light source optical system according to claim 1, wherein thelight guide element is configured to guide the portion of the secondlight beam to be farther from an optical axis of the second opticalsystem.
 12. A light source unit comprising: a first optical systemthrough which a first light beam emitted from a light source passes; awavelength conversion element configured to wavelength-convert the firstlight beam passed through the first optical system into a second lightbeam; and a second optical system through which the second light beampasses, the second optical system including a light guide elementthrough which a portion of the second light beam passes.
 13. An imagedisplay apparatus comprising: a light source device including: a lightsource to emit a first light beam having a first wavelength; a firstoptical system configured to guide the first light beam emitted from thelight source to a wavelength conversion element; the wavelengthconversion element configured to convert the first light beam into asecond light beam having a second wavelength different from the firstwavelength, and emit the second light beam; and a second optical systemthrough which the second light beam passes, the second optical systemincluding a light guide element configured to guide a portion of thesecond light beam from one end surface of the light guide element to theother end surface of the light guide element to separate the portion ofthe second light beam from the second light beam; an image displayelement configured to modulate light from the light source device toform an image; and a projection optical system configured to project theimage onto a projection surface.